It has been longer than I expected to do my first Gentoo install. I have been using Linux since 1999. I have done some research to prepare myself for installing Gentoo.

Research suggests for a first time Gentoo install the time it takes is varied due to the learning curve. Though I have never used Gentoo I am familiar with building from source the likes of KDE, Gnome, Firefox, GTK, more kernels that I can count, LXDE, OpenBox, and most of the applications one could ever use. I know for example the image processing software I use can actually take longer than kernel, Firefox, KDE, Gome combined even though the size of the source code for the imaging software is much smaller. It seems the complexity of the imaging software is the reason for the long involved compile times.

The question I have is for a Intel T5600 laptop with a SATA 1 drive 4GB RAM what the best case guess for compile time from zero to LXDE, Firefox, Sylpheed, Gnome-Terminal, LeafPad, LXTerminal, PCmanFM, Geany, Gedit, Gparted, and GIMP? I am more than aware from manually building from source these programs a number of times over the years, and many more, that this implies a number of other packages and libraries. I certainly have alot more installed on my system than this list, but this would be my starting point to be up and running. There are certainly other packages I would also install, but know they will not take alot of time in comparison to compile or have complex dependencies, hence this short list to for a basic time estimate from zero to up to a working set of programs to enable me to transfer over my work and primary working distribution.

One other question which I have not been able to figure out from reading and searching is if I can use, likely via a USB flash drive, a copy of my existing kernel configuration for the 3.4.x Linux kernel and will be able to run the make oldconfig to update the config to the 3.4.x Linux kernel I choose to start with in Gentoo? I currently use a Kernel.org Linux stock kernel 3.4.x series. I am about to compile 3.4.39 on my existing system as it seems many important changes for me have been made since 3.4.24 and 3.4.24 has a number of problem bugs I have never seen in a kernel before. I have all of my kernel configurations for 3.4.x all the way back to 3.4.9 just in case.

You can ask us to provide a build time for a program, but asking build time with dependencies is something undoable. At first because you may think a dependency is a library for that program, while for gentoo dependencies start at gcc, binutils... And so your answer is highly impossible to answer, as it depend what dependencies are already install in your system to endup with gnome-terminal per example. A user that have a printer have more dependencies than someone without one...
Here's an output of all dependencies i have for gnome-terminal

Code:

emerge -pve gnome-terminal | grep "\[ebuild" -c
392

So the best human answer is: a shit load of time.
The best compute estimate by genlop is: Estimated update time: 5 hours, 4 minutes.
Here's the output for gnome-terminal only (just that program, 0 deps):

But as soon as your system is running build time is gone to 0, you have gnome-terminal-1 and portage build gnome-terminal-2 and when finish, portage will remove the 1 and replace it with the 2, if you are waiting for the 2, yes, you will feel the wait. But if you just do your work, you will see gnome-terminal is now v2 while you were using v1 just before.

We have the vanilla kenrel, just so you don't have to download it yourself, eheh how lazzy
We have a "gentoo" kernel, that is a vanilla kernel and some patch by our devs and community to fix/add... the kernel, but it's just a vanilla kernel. Basically the gentoo kernel is the same as kernel.org one, except one guy do the work to add patchs... for all others.
And we have some more kernels, this time, more specific, that this time could be far from the vanilla kernel.